QCM sensors for detecting volatile organic compounds (VOCs): A review of mechanisms, coatings, and applications.

Quartz crystal microbalance (QCM) sensors are highly sensitive and low-power tools for detecting volatile organic compounds (VOCs). This review article addresses the operating principles of QCM, factors affecting gas adsorption, and various sensitive coatings including smart polymers, nanoporous materials (MOFs and zeolites), ionic liquids, graphene and nanocomposites, nanoparticles, and biological systems. Applications of these sensors in air quality monitoring, food industry, disease diagnosis via breath analysis, and security/military sectors are discussed, along with performance limitations such as humidity interference, long-term stability, and slow recovery. The role of multi-channel QCM (MQCM) systems and advanced data analysis techniques like PCA and LDA in simultaneous detection of multiple VOCs is also highlighted. Results indicate that the design of multi-component coatings, use of novel materials, and implementation of machine learning algorithms significantly enhance sensor sensitivity, selectivity, and stability. Combining nanomaterials, low-power electronics, and artificial intelligence is expected to transform future QCM sensors into smart, portable, and accurate devices for real-time VOC monitoring.